We have succeeded in using a multiwire proportional chamber (30 cm x 30cm) together with its electronic readout into a large core memory (mass core) as a digital area detector for protein crystallography. This area detector is part of a high-speed data collection system to be used in the determination of protein structure by the X-ray diffraction method. The diffraction pattern stored in the mass core can be displayed on a TV monitor. An IBM 1800 computer has fast random access to the mass core and is used on line to estimate the integrated reflection intensities. To characterize this new area detector, we have measured the geometric linearity, the resolution and the quantum detection uniformity. Preliminary results show that with this new system one can collect intensity data from protein crystals about an order of magnitude faster than with the standard diffractometer. The precision of the new data is also better than the ones collected with standard diffractometer and precision camera. We plan to make further improvements to the system and to use it to collect very high resolution data for four proteins and enzymes; subtilisin, HiPIP, cytochrome C2 and chymotrypsinogen.